This invention relates, in general, to Digital to Analog Converters (DACs), and more particularly, to a switchable current source for reducing noise glitches in a Digital to Analog Converter.
A Digital to Analog Converter (DAC) is an electronic circuit that converts a digital signal to an analog signal. In general, a numerical value of the digital signal input to a DAC corresponds to a magnitude of the analog signal output by the DAC. The speed of at which a DAC converts a digital signal to a stable analog signal is an important parameter for many circuit applications. A second factor is the resolution of a DAC. The resolution of a DAC is the smallest incremental signal that is generated and corresponds to the Least Significant Bit (LSB) of an input digital signal. A third factor is noise generated by a DAC as a conversion takes place.
One area that utilizes high speed, high resolution, Digital to Analog Converters is the communication industry, for example, cellular phones. High frequency glitches generated by a DAC produce spurs or distortion that can be received by other communication circuits which could produce errors in reception. The high frequency glitches are generated as the DAC produces an output signal change. In general, the high frequency glitches are produced by delay differences between the individual circuits that produce voltages or currents that are summed together to generate the analog output signal. Spurious free dynamic range is a measure of glitch caused distortion that is specified for DACs used in these types of applications to reduce reception errors.
It would be of great benefit if a switchable current source could be provided for reducing noise generated by a Digital to Analog Converter.